Description of quantum effects in the condensed phase

Recent experiments on light harvesting complexes have shown clear indication of coherent transport of excitations in these aggregates. We review the theoretical models that have been used to study energy transfer in molecular aggregates, beginning with the early models of Förster and Davydov. We cover the Redfield and Haken Strobl models in some detail, in order to set the nomenclature and because they are the most common and easiest models to understand and work with. We briefly discuss more complex models.